I think it's fair to criticize people who can't perform at their jobs.
Ben Simmons has chosen professional basketball. He chose to accept a $40 million / year contract. He chose to sit out with the Sixers. He chose to malinger at practices. If he experiences crippling anxiety or other mental illness, that's not necessarily a "fault" or something he has control of. However, fans can criticize him for choosing a career that he's unable to perform at. If you can't meet the core expectations of the job, retire.
And, I do see it as similar to Simone Biles. She accepted the endorsement money. She billed herself as the GOAT, branding merchandise that she profited off of. If she can't mentally perform at the highest level, it's something that should be held against her when judging her legacy. The mental illness isn't a choice or a fault, but the marketing is.
Not every person is suited to their career, even if they're talented at it. You need the entire constellation of talents to be an athlete, and that means being free from mental setbacks. It's no different than a lawyer or a chef or a truck driver: if the pressures of the job are causing you to fail at it, and counseling / medication aren't alleviating the problem, then maybe it's time to pick a different career.